Field of the Invention
The present invention relates to an image capturing apparatus and a method of controlling the same.
Description of the Related Art
An aberration called a curvature of field occurs in imaging optical systems used in image capturing apparatuses such as digital cameras, whereby a shift in image forming positions occurs in the optical axis direction between the central portion and the peripheral portion of the image sensing plane. For this reason, conventionally, correction is performed such that the curvature of field aberration is reduced with an optical system configuration in which a plurality of lenses are combined. In contrast to this, recently, image sensors have been proposed in which the aforementioned curvature of field aberration is corrected by curving the image sensor itself, that is, the image sensing plane. It is conceivable that curving the image sensing plane to correct the curvature of field aberration allows for simplification of the optical system, and that the necessity to combine a large number of lenses is reduced.
Also, many cameras are equipped with an optical zoom function and the zoom lens position differs according to the zoom magnification rate, and thus the state of the curvature of field also varies. In contrast to this, technology that controls the curvature to which the image sensing plane is curved according to the state of the curvature of field has been proposed (Japanese Patent Laid-Open No. 2012-182194).
Dark current generally occurs in image sensors and there are cases where noise caused by dark current is prominent, particularly during periods of high sensitivity and long exposure times, and therefore various types of noise reduction processing are executed. On the other hand, it is known that, in an image sensor with a curved image sensing plane, dark current that occurs in the image sensor is reduced by tensile stress when the image sensor is curved.
However, as described in Japanese Patent Laid-Open No. 2012-182194, the amount by which dark current is reduced varies when the curvature at which the image sensing plane is curved is varied according to the zoom magnification rate, and there are cases where noise cannot be sufficiently reduced, even if noise reduction processing is performed.